Evaluation of the Efficacy of Titanium Mesh Cages with Posterior C1 Lateral Mass and C2 Pedicle Screw Fixation in Patients with Atlantoaxial Instability

Biomechanical Effects of Lateral Inclination C1 and C2 Pedicle Screws on Atlantoaxial Fixation

Objective

To assess the biomechanical effect of lateral inclination C₁ and C₂ pedicle screws on the atlantoaxial fixation through vitro human cadaveric study.

Methods

From January 2016 to December 2017, fresh‐frozen cadaveric cervical spines with intact ligaments from eight donated cadavers at an average age of 71.5 ± 10.6 years, comprising of six males and two females, were collected. There were no fracture and congenital malformation in all specimens according to the imaging examination. The range of motion (ROM) of the specimens were tested in their intact condition and destabilized condition. Next, the specimens were randomly divided into two groups to ensure no differences in sex and age: Group 1 was medial inclination C₁ pedicle screw and C₂ pedicle screws (C₁MPS‐C₂PS) and Group 2 was lateral inclination C₁ pedicle screw and C₂ pedicle screws (C₁LPS‐C₂PS). The ROM of the fixation scenarios were recorded. Thereafter, all the specimens with fixation constructs were tested for 1,000 cycles of axial rotation and tensile loading to failure was carried out collinearly to the longitudinal axis of all the screws, the data were documented as screw pullout strength (SPS) in newtons. All the recorded data subjected to quantitative analysis.

Results

The ROM of specimens was increased significantly in destabilized condition and significantly reduced in fixation condition compared with intact condition. In C₁LPS‐C₂PS groups, the C₁‐C₂ cervical segment showed 3.96° ±1.21° and 3.75° ± 1.33° in flexion and extension direction, 2.85° ± 0.91° and 2.96° ± 0.71° in right and left lateral bending, 2.20° ± 0.43° and 2.15° ± 0.40° in right and left axial rotation. In C₁MPS‐C₂PS groups, it showed 4.24° ±1.31° and 3.98° ± 1.21° in flexion and extension direction, 2.76° ± 1.10° and 3.23° ± 0.62° in right and left lateral bending, 2.20° ± 0.46° and 2.21° ± 0.42° in right and left axial rotation. There was no statistically significant difference on ROM and screw pullout strengths (764.29 ± 129.00 N vs 714.55 ± 164.63 N) between the two groups. However, there was one specimen in the C₁MPS‐C₂PS group showing rupture the inferior wall of the left screw trajectory owing to the relatively thin posterior arch of the atlas, the screw pullout strength was significantly reduced (left pullout strength value: 430.5 N, right pullout strength value: 748.4 N). Therefore, in the case of the thin posterior arch of the atlas, the C₁LPS‐C₂PS group had strong long‐term biomechanics.

Conclusion

The lateral inclination C₁ pedicle screw can achieve the same biomechanical strength as the traditional atlas pedicle screw. However, for the case where the posterior arch of the atlas is relatively thin, a lateral inclination C₁ pedicle screw is more suitable.

Regenerative Materials for Surgical Reconstruction: Current Spectrum of Materials and a Proposed Method for Classification

Chronic wound management is an enormous economic strain and quality-of-life issue for patients. Current treatments are ineffective or expensive and invasive. Materials (native and artificial) can act as the basis to enhance wound repair but often fall short of complete healing. The therapeutic index of materials have often been enhanced by combining them with drug or biologic elution technologies. Combination of materials with living drugs (cells) presents a new paradigm for enhancing therapy. Cell material interaction and therapeutic output will depend on variables ascribed to the living drug as well as variables ascribed to the underlying matrix. In this article, we review medical matrices currently approved by the US Food and Drug Administration (FDA) that would likely be the first generation of materials to be used in this manner. Currently there are hundreds of different materials on the market. Identification of the right combinations would benefit from a classification scheme to group materials with similar composition or derivation. We provide a classification scheme and FDA documentation references that should provide researchers and clinicians a starting point for testing these materials in the laboratory and rapidly transitioning cell therapies to the bedside.

Usefulness of titanium mesh cage for posterior C1-C2 fixation in patients with atlantoaxial instability

The aim of this study was to investigate the usefulness of titanium mesh cage as an interlaminar spacer combined with nitinol shape memory loop fixation in patients with atlantoaxial instability.From April 2009 to March 2017, among the patients with atlantoaxial instability, a total of 30 patients were treated by nitinol shape memory loop fixation combined with titanium mesh cage as a spacer. We retrospectively reviewed 30 enrolled patients. Successful fusion was determined as improvement of symptoms and radiologic findings of bone fusion. We also reviewed surgical complications, instrumentation failure, bony fusion rate, and posterior atlantodental interval (PADI).After surgery, the symptoms of all patients significantly improved. Successful fusion was documented throughout the follow-up period. Evidence of solid bridging bone was found, and no instability was seen on flexion-extension radiographs and callus formation on 3D cervical spine computed tomography (CT) 6 months postoperatively in all cases. No surgical complications were observed. No cases of instrumentation failure were observed. The mean PADI also improved significantly to 22.45 ± 1.11 mm 6 months postoperatively compared with the preoperative value of 18.37 ± 1.16 mm (P < .05).We obtained a good fusion rate by using titanium mesh cage spacer with nitinol shape memory alloy loop in patients with atlantoaxial instability. This technique can help surgeons in avoiding vertebral artery injury and reducing bleeding and operation time. Therefore, we suggest that titanium mesh cage spacer combined with nitinol shape memory alloy loop can be a good substitute of autograft for C1-C2 fusion in treating atlantoaxial instabilities.

The Effects of Clinical Factors and Retro-Odontoid Soft Tissue Thickness on Atlantoaxial Instability in Patients with Rheumatoid Arthritis

BACKGROUND

Rheumatoid arthritis (RA) is an autoimmune disease that often occurs in the atlantoaxial segment of the cervical spine and results in instability that can cause severe pain and neurologic symptoms. Thickening of soft tissue posterior to the odontoid process of the atlantoaxial segment is referred to as retro-odontoid soft tissue (ROST) thickness or pseudotumor. The mechanism of ROST thickness is still unknown.

METHODS

Among patients diagnosed with RA, those with cervical radiographs and magnetic resonance imaging records were selected for investigation of their clinical symptoms, laboratory findings, radiologic evaluation, and RA medication history.

RESULTS

A total of 199 patients were selected and divided into lower and upper median groups according to the ROST thickness value. In patients with RA, the median ROST thickness value was 2.3 mm (interquartile range, 1.4-3.4). The median value of the anterior atlanto-dens interval (ADI) was 2.4 mm, with a significant difference being observed between the lower and upper median ROST thickness groups (P = 0.001). Multivariable linear regression analysis revealed a correlation between Steinbrocker stage and the positivity of rheumatoid factor. For each unit increase in the Steinbrocker stage, the ROST thickness increased by 0.35 mm (β, -0.349; 95% confidence interval -0.643 to -0.055; P = 0.020). For every 1-mm increase in the ADI, ROST thickness decreased by 0.16 mm (β, -0.163; 95% confidence interval -0.264 to -0.062; P = 0.002).

CONCLUSIONS

This study showed a statistical correlation between ROST thickness and ADI related to biomechanical changes in the dynamic atlantoaxial segment, thereby suggesting the value of a prospective study.